LOW-TEMPERATURE SINTERING OF ZnO-Bi₂O₃-BASED VARISTOR CERAMICS FOR ENHANCED MICROSTRUCTURE DEVELOPMENT AND CURRENT-VOLTAGE CHARACTERISTICS

Abstract

ZnO-Bi₂O₃-based varistor ceramics are typically sintered at temperatures above 1100 °C to ensure the proper microstructure development and the required current-voltage (I-U) characteristics. In this investigation the influence of the sintering regime at temperatures between 800 and 950 °C on the microstructure development and the I-U characteristics of varistor ceramics was studied. It was shown that the presence of a sufficient amount of Bi₂O₃-based liquid phase at the proper Sb₂O₃-to-Bi₂O₃ ratio enhanced the sintering and also promoted grain growth under the influence of the inversion boundaries (IBs) triggered in the ZnO grains by the Sb₂O₃. The well-developed microstructures with high density and grain sizes from 4 to 8 μm resulted in good current-voltage characteristics of the samples with a coefficient of nonlinearity α equal to about 30 and a low leakage current IL of below 1 μA. Depending on the composition and the sintering regime, the threshold voltages VT were in the applicable range from 270V/mm to 850V/mm, even though values much greater than 1000V/mm are typically obtained with such low sintering temperatures.

Keywords

• ZnO
• Varistor ceramics
• Sintering
• Microstructure
• Electrical characteristics